Electric actuators such as motors or solenoids have been extensively used for converting an electric signal into a mechanical motion or a hydraulic pressure as various objects to be controlled are electronically controlled. In order to upgrade those electric actuators, a high-precision current control is essential. In recent years, for the purpose of conducting a high-precision current control, it is general to use a digital feedback control.
For the purpose of conducting a current digital feedback control, there is a need to acquire a digital value Ioutd of a load current value Iout to be controlled. To achieve this, an output Vout of a current-voltage converter circuit is subjected to digital conversion by an AD converter to obtain a relative digital value Voutd (=Vout/Vref) to a reference voltage Vref of the AD converter. Then, the output Voutd of the AD converter is subjected to a correction corresponding to an input/output characteristic of a current detector circuit including the current-voltage converter circuit and the AD converter to obtain the digital value Ioutd of the current.
Various configurations of the current detector circuit have been proposed. From the viewpoint of simplifying a control algorithm, it is desirable to make the input/output characteristic of the current detector circuit linear, and in this case, the current digital value Ioutd is obtained by Expression (1) with the use of a gain a and an offset b.Ioutd=a·Voutd+b  (1)
When the current value is measured according to Expression (1), it is important how the gain a and the offset b match the characteristic of a real current detector circuit with high precision, for the purpose of improving a current measurement precision.
Also, needs of the downsized control device and the lower prices are high in addition to the high-precision current control, and the current detector circuit is incorporated into an IC chip to respond to those needs. A current detection resistor incorporated into the IC chip to incorporate the current detector circuit into the IC chip has been known (for example, refer to PTL 1 and PTL 2).